Diesel engine operation involves combustion that generates exhaust gas. During combustion, an air/fuel mixture is delivered through an intake valve to cylinders and is combusted therein. Air flow delivered to the cylinders can be measured using a mass air flow (MAF) sensor. The MAF sensor measures the total intake fresh air flow through the air induction system. After combustion, the piston forces exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain various emission components including diesel particulates or soot.
A diesel particulate filter (DPF), usually disposed in the exhaust stream, can be used to reduce the level of soot in the exhaust gas. As soot accumulation increases within the DPF, pressure increases inside the DPF which increases backpressure (BP) within the engine. An increase in BP may result in a loss of air flow to the engine. A variable geometry turbo (VGT) is employed to compensate for the loss in air flow by controlling the intake manifold pressure (boost) to the engine. The VGT has moveable vanes that are located in the turbine housing and that enable the VGT to control boost by managing exhaust turbine inlet pressure. As BP increases, an increasingly greater amount of boost may be required to maintain engine operation at specific conditions.
Over time, the DPF becomes full of soot and is regenerated to remove the trapped diesel particulates. During regeneration, the diesel particulates are burned within the DPF to renew the filtering function of the DPF.
Engine systems often include an exhaust gas recirculation (EGR) system to reduce engine emissions. EGR involves re-circulating exhaust gases back into the cylinders, which reduces the amount of oxygen available for combustion and lowers cylinder temperatures. For exhaust gas to flow into the intake manifold, exhaust pressure must be greater than the intake manifold pressure (boost). An EGR system enables ignition timing to remain at an optimum point, which improves fuel economy and/or performance. However, debris build-up within the EGR system may restrict exhaust flow there through and minimize the effectiveness of the EGR system. In addition, as BP increases the EGR mass flow may need to be reduced to maintain performance.